Fatty acid synthase (FAS) is a 270 kDa cytosolic protein that functions as a homodimer. (1) FAS is expressed in low to undetectable levels in most normal human tissues. (2) In contrast, FAS is overexpressed in a large number of human cancers, including prostate cancer, despite high levels of ambient fatty acids, and its overexpression has been associated with poor prognosis. (3-6) In prostate cancer, FAS is overexpressed throughout the natural history of a majority of tumors beginning with prostatic intraepithelial neoplasia (PIN). (3) Although the biochemical and metabolic basis for FAS overexpression in tumor cells in not well understood, it appears that FAS overexpression confers a selective growth advantage to tumor cells. Prostate tumors expressing high FAS levels display aggressive biologic behavior. (7)(8)
Prostate-specific antigen (PSA) is used as a biological or tumor marker to detect prostate disease. PSA is a protein produced by cells of the prostate gland. The PSA test measures the level of PSA in the blood; but PSA alone is not a reliable indicator of the presence of prostate disease.
It is normal for men to have a low level of PSA in their blood. The reference range of PSA is between 0-4.0 ng/mL, based on a study that found 99% of a cohort of apparently healthy men had a total PSA level below 4 ng/mL; the upper limit of normal is much less than 4 ng/mL. (9)(10) Increased levels of PSA may suggest the presence of prostate cancer; however, prostate cancer can also be present in the complete absence of an elevated PSA level, in which case the test result would be a false negative. (9)
As men age, both benign prostate conditions and prostate cancer become more common, resulting in an increase in PSA levels. PSA levels can be increased by conditions including prostate infection, irritation or benign prostatic hyperplasia (BPH). (11)(12) According to the National Cancer Institute, PSA levels alone do not give doctors enough information to distinguish between benign prostate conditions and cancer. Treatment needs to be individualized based on the individual's risk of progression as well as the likelihood of success and the risks of the treatment. (13)